1. Field of the Invention
The present invention relates to image sensing apparatuses, and more particularly to image sensing apparatuses capable of performing an image sensing operation with an increased frame rate.
2. Description of the Related Art
In recent years, image sensing apparatuses such as digital still cameras and digital video cameras have been increasing the number of pixels of an image sensor thereof. As being represented by a complementary metal-oxide semiconductor (CMOS) sensor, sensors of an XY-address type provided with an amplifier for each pixel have being greatly developed.
Regarding operations of the sensors, Japanese Patent Application Laid-Open No. 01-154678 discusses a technique for subtracting signals generated when an input of the pixel to the amplifier is reset from pixel signals to eliminate a noise.
For example, when the pixel signals in one horizontal line are read out, the input of the pixels in the one horizontal line to the amplifier is reset. The generated signals in the one horizontal line when the input is reset are stored as noise signals. The pixel signals in the one horizontal line are read out and stored separately from the noise signals. A paired pixel signal and noise signal for each pixel are output from the sensor. By subtracting the noise signals from the pixel signals, the image signals having a reduced noise can be acquired.
Regarding recording of a moving image, a mainstream has been changing to the high definition (HD) (1920×1080 pixels) of a standard image size for a moving image from the Quarter Video Graphic Array (QVGA) (320×240 pixels) or the Video Graphics Array (VGA) (640×480 pixels) owing to the increasing number of pixels of an image sensor. Therefore, a moving image is recorded at a higher resolution than ever without decreasing the frame rate.
However, according to Japanese Patent Application Laid-Open No. 01-154678, since reading out the noise signal and the pixel signal is performed, an operation time for reading out the image increases. Thus, when considering the frame rate, the time for reading out the image may not be sufficiently provided for recording the high definition (HD) moving image.